1. Field of the Invention
This invention relates to a headbox for ejecting stock onto a forming wire of a papermaking machine. More particularly, this invention relates to a headbox including a slice chamber for the passage therethrough of a primary flow of stock and means for injecting a secondary flow of stock laterally relative to the primary flow.
2. Information Disclosure Statement
In the manufacture of a web of paper or board, a slurry of randomly oriented fibers is ejected from a headbox onto a moving screen or forming wire. Water is drained, or otherwise removed, from the layer deposited on the screen. This formed web is then pressed between cooperating surfaces in order to remove excess moisture from the formed web. Thereafter, the pressed web is guided around a plurality of drying cylinders in order to produce a web having the desired characteristics.
In the formation of a fibrous mat, the fiber orientation within the mat is generally controlled by the jet-to-forming-wire-speed relationship. According to the type of paper or board being produced, such fiber orientation may be caused to a greater or lesser degree so that fiber orientation in a machine-direction may be controlled. The fiber orientation within a typical news sheet can be demonstrated by tearing the sheet in the machine and cross-machine direction. Such sheet tears relatively easily in a machine-direction. However, more resistance to tearing is observable when endeavoring to tear the same news sheet in a cross-machine direction. This variation in tear strength in a machine and cross-machine direction is important relative to the production of newsprint. However, a particular problem exists due to this variation, particularly with regard to the formation of the edges of the formed web.
More particularly, there exists a tendency for the individual fibers within the stock to be deposited in a generally machine-direction orientation. However, at the respective edges of the sheet, the individual fibers tend to spread out to present a fan-shaped orientation. This machine-direction orientation tends to cause wrinkling of the edges of the sheet when these edges pass through the dryer section. Such wrinkling is caused mainly because, as the web is dried, a non-uniform shrinkage occurs in a cross-machine direction due to the lack of fibers deposited in a cross-machine direction.
Various devices have been proposed in an attempt to reorient the fibers within a web such that the fibers at the edges of the web are dispersed parallel to the fibers dispersed in a generally directed machine-direction. However, these prior proposals have been relatively complex and costly and have met with only limited success.
The present invention provides a simple and inexpensive means for orienting the fibers, particularly adjacent to the edges of the web, by injecting a secondary flow of stock laterally into the slice chamber of a headbox such that the tendency for the fibers disposed at the edges of the web to fan out relative to those fibers disposed between the edges is inhibited.
Therefore, it is a primary object of the present invention to provide an apparatus that overcomes the aforementioned inadequacies of the prior art proposals by providing a headbox having means for injecting a secondary flow of stock laterally relative to the primary flow of stock for controlling fiber orientation along the lateral side edges of the stock ejected from the headbox onto the forming wire.
Another object of the present invention is the provision of a headbox having a first and second conduit connected respectively to the first and the second side walls of the headbox for conducting the secondary flow through the side walls into the slice chamber.
Another object of the present invention is the provision of a headbox in which the means for injecting the secondary flow also includes a first and a second valve for controlling the secondary flow through the respective side walls.
Another object of the present invention is the provision of a headbox in which the means for injecting the secondary flow also includes a first and a second flowmeter for measuring the secondary flow through the first and second conduits respectively.
Another object of the present invention is the provision of a headbox in which the secondary flow is injected at an acute angle relative to the respective side walls.
Another object of the present invention is the provision of a headbox in which the general direction of the primary flow and the secondary flow are disposed in the same plane.
Another object of the present invention is the provision of a headbox in which the secondary flow is injected laterally into the primary flow along the entire distance between the upper and the lower wall of the headbox.
Another object of the present invention is the provision of a headbox in which the secondary flow is injected laterally through the side walls into the slice chamber for controlling the orientation of fibers within the primary flow such that along the lateral side edges, the fibers are reoriented so that as the stock is ejected from the headbox onto the forming wire, the lateral edges will be subjected to more uniform shrinkage and uniform physical properties.
Another object of the present invention is the provision of a headbox in which the angle at which the secondary flow is injected into the primary flow may be adjusted to selectively generate clockwise and counter-clockwise orientation of the fibers adjacent to the lateral side edges.
Another object of the present invention is the provision of a method for ejecting the stock from a headbox onto a forming wire of a papermaking machine, the method including the steps of passing the stock in a primary flow through a slice chamber and injecting a secondary flow of stock laterally relative to the primary flow such that the secondary flow controls the fiber orientation along the lateral side edges of the stock ejected from the headbox onto the forming wire.
Other objects and advantages of the present invention will be apparent to those skilled in the art from a study of the detailed description taken in conjunction with the drawings and from a consideration of the appended claims which define the scope of the present invention.